A Web-Based Introduction to Programming

1. A Web-Based Introduction to Programming Chapter 12 Associative Arrays Chapter 12

2. Intended Learning Outcomes • Summarize key characteristics of associative arrays. • Create an associative array. • Identify useful applications for associative arrays. • Use a literal key value to access a value in an associative array. • Use a variable that contains a key value to access a value in an associative array. • Describe the structure of the PHP $_POST array. • Summarize the basic characteristics of a Web session • Create and destroy a Web session. • Use the $_SESSION array to share variables between pages Chapter 12

3. Introduction • Chapter 11 demonstrated the structure and use of arrays that are indexed with numerical values. • Many languages, including PHP, also permit the use of associativearrays… Chapter 12

4. Associative Arrays • An associative array is indexed with character strings (keys) that describe the content of each element (values). For example: $scores['Exam 1'] = 90; $scores['Exam 2'] = 93; $scores['Exam 3'] = 87; $scores['Essay'] = 78; $scores['Project'] = 80; • In the first element, 'Exam 1' is a key, 90 is a value. Chapter 12

5. Associative Arrays • Associative Arrays are especially useful for lookups.. • Associative arrays have limited uses. They are only useful when: • Meaningful key names can be provided for each array element. • The array contains a relatively small number of values. Chapter 12

6. Looking up a Value Using a Key We can use an associative array as a lookup by referencing a particular array key, for example to lookup a user password from an array where the keys are user IDs: $userList ['mike75'] = "abc123"; $userList ['mary2'] = "xyz999"; $userList ['chris17'] = "abc999"; print("<p>The password for user chris17 is $userList['chris17']</p>"); Chapter 12

7. Using a Variable to Reference a Key Value It is often useful to use a variable to look up an array value. For example we can obtain a user ID from an HTML form and use this as the key to test the user password in the $userList array: $userList ['mike75'] = "abc123"; $userList ['mary2'] = "xyz999"; $userList ['chris17'] = "abc999"; $id = $_POST['id'] ; $password = $_POST['password '] ; if ($userList ['$id'] == $password) print("<p>WELCOME $id!</p>"); else print("<p>YOUR LOGIN FAILED</p>"); Chapter 12

8. Another Example: Company Information • Using an associative array to store important company information $companyInfo ['name'] = "Most Excellent Web Design, Inc."; $companyInfo ['street'] = "123 Main Street"; $companyInfo ['city'] = "Sometown"; $companyInfo ['state'] = "SomeState"; $companyInfo ['zip'] = "12345"; $companyInfo ['email'] = "excellent@mewd.com"; $companyInfo ['phone'] = "(123) 456-7890"; $companyInfo ['fax'] = "(098) 765-4321"; Chapter 12

9. Another example: Countries and Capitals $capitals['FRANCE'] = "PARIS"; $capitals['ENGLAND'] = "LONDON"; $capitals['AFGHANISTAN'] = "KABUL"; $capitals['ANGOLA'] = "LUANDA"; $capitals['BOLIVIA'] = "SUCRE"; $country = $_POST[‘country']; print("<p>The capital of $country is $capitals[$country]</p>"); Chapter 12

10. Using the array() Function to Create Associative Arrays • The PHP array() function can be used to create associative arrays using the => operator to associate keys and values: $capitals = array ('FRANCE' => "PARIS", 'ENGLAND' => "LONDON", 'AFGHANISTAN' => "KABUL", ‘ANGOLA' => "LUANDA“, 'BOLIVIA' => "SUCRE"); • This is equivalent to assigning each array element separately (previous slide) Chapter 12

11. More About the $_POST Array • PHP defines a number of standard associative arrays. • Identified by $_ at the beginning of the array name. • The $_POSTarray is an example. • When a user submits a form using method = "post" attribute, a $_POST array is created for the program that will process the form. • The keys of the $_POST array are the names associated with each input field in the form • The values in the $_POST array are the valuessubmitted by the user in these fields. Chapter 12

12. More About the $_POST Array • Example: <form action = "wage2.php" method = "post" > <p>Please enter your hourly wage: <input type = "text" size = "20" name = "hourlyWage" /></p> <p>And the hours you have worked: <input type = "text" size = "20" name = "hoursWorked" /></p> <input type = "submit" value = "Wage Report " /> </form> Chapter 12

13. More About the $_POST Array • The method is "post" so the server provides wage2.php with a $_POST array with the values submitted by the user. • Each value in the $_POST array is indexed with the names from the HTML form fields: • $_POST ['hourlyWage']contains the value submitted by the user in the field named "hourlyWage".  • $_POST ['hoursWorked']contains the value submitted by the user in the field named "hoursWorked". Chapter 12

14. More About the $_POST Array • Our code examples always retrieve values from the $_POSTarray and store them in program variables: $hourlyWage = $_POST['hourlyWage']; $hoursWorked = $_POST['hoursWorked']; $pay = $hourlyWage * $hoursWorked; • But we can also use the elements of the $_POST array directly without any need for additional variables: $pay = $_POST['hourlyWage'] * $_POST['hoursWorked']; Chapter 12

15. The $_GET and $_REQUEST Arrays • The $_GETarray is used when the method attribute of the HTML <form> tag is assigned the value "get". • Less secure (values are submitted as part of the URL). • Limits the number of characters that can be submitted. • The $_REQUESTarray will receive form values whether the <form> attribute is "get" or "post". • Good choice when a program handles input from multiple sources, where it may not be known whether the input is submitted using the "get" or "post" method. Chapter 12

16. Using the isset() Function • The isset() function tests whether or not a variable has already been created. if(isset($someVariable)) • This is not the same as the empty() function: if(empty($someVariable)) • The empty() function tests whether or not a variable contains a value, the isset() function tests whether or not the variable exists. Chapter 12

17. Using the isset() Function to Process HTML Forms • The isset() function can be used to combine an HTML form with the code to process the form on the same page. • For example if an HTML form contains a text input named 'age', you can test whether or not this element exists in your $_POST array: if(isset($_POST['age'])) • This will indicate whether or not a form containing 'age' has been submitted. Chapter 12

18. Using the isset() Function to Process HTML Forms • By testing if $_POST contains values, a page can choose to display or process the form: if (isset($_POST['age'])) { // statements to process this form } else { // display the form } Chapter 12

19. CODE EXAMPLE:addTwoImproved.php Chapter 12

20. CODE EXAMPLE:addTwoImproved.php if (isset($_POST['number1'])) { $number1 = $_POST['number1']; $number2 = $_POST['number2']; $result = $number1 + $number2; print ("<h1> RESULTS </h1>"); print (" <p>$number1 + $number2 = $result.</p> "); print (" <p><a href = \"addTwoImproved.php\"> Return to the Input Form</a></p> "); } // See next slide for the ELSE section.. Chapter 12

21. CODE EXAMPLE:addTwoImproved.php // continues from previous slide else { print ("<h1>ADD TWO NUMBERS</h1> <form action = \"addTwoImproved.php\" method = \"post\" > <p>1st number: <input type=\"text\" size=\"20\“ name=\"number1\" /></p> <p>2nd number: <input type=\"text\" size=\"20\" name=\"number2\" /></p> <p><input type = \"submit\" value = \"Tell me the sum\" name = \"submit\" /></p> </form>"); } Chapter 12

22. Web Sessions and the $_SESSION array • A Web session allows data to be maintained beyond the life of a single Web page. • The data can be accessed and modified by multiple pages, as long as the session is running. • In PHP, a Web session is started using session_start(), and ended using session_destroy(). • A session also ends if the user closes all open windows of the browser. • The data for the session is stored in a standardassociativearray named$_SESSION. • Each user's data is maintained separately. Chapter 12

23. Associating Web Pages with a Session • Everypage (not just your intended starting page) mustinclude a call to start_session() in a PHP section • This statement must appear beforeany HTML tags that appear in the file: <php session_start(); ?>  <html> ... HTML and additional PHP code here..  </html> Chapter 12

24. Working with Session Variables • Elements can be added to the $_SESSION array whenever needed, just like any other array: $_SESSION['playerName'] = $_POST['playerName']; $_SESSION['playerScore'] = 0; • $_SESSION elements can be accessed and modified by any page that includes a call to session_start(), for example: print ("<h1>PLAYER: ".$_SESSION['playerName']."</h1>"); $_SESSION['playerScore'] = $_SESSION['playerScore'] + 10; Chapter 12

25. Ending the Session • Use the session_destroy()function. All session data is lost at this time. • If the user returns to a page that includes a call to the session_start()function, after the session has been ended, a new session will be created at that time. • The session will also end if the user closes all of their browser's open windows. Chapter 12

26. A Simple Example: Raffle • Look at the following three files in the sessions folder, located in your samples folder: raffle.html, raffle.php, choosePrize.php. • To submit a raffle ticket number open raffle.html. Chapter 12

27. Raffle Screenshots Chapter 12

28. Raffle Screenshots Chapter 12

29. Coding Raffle • Review the Raffle application code carefully • Note how the player’s name and city are stored in the $_SESSION array so these values can be accessed by choosePrize.php. • Note that all pages use session_start() to participate in the session. • Note that choosePrize.php includes session_destroy() to end the session. Chapter 12

30. A Small Game Example: Goldhunter • Look at the following three files in the sessions folder, located in your samples folder: goldHunter.html, goldHunter1.php, goldHunter2.php. • To play the game open goldHunter.html. Complete the game to destroy the session. • Try playing without entering a user name. • Try starting the game by opening goldHunter1.php or goldHunter2.php instead of goldHunter.html Chapter 12

31. GoldHunter Screenshots Chapter 12

32. GoldHunter Screenshots Chapter 12

33. Another Session Example: Online Quiz (tracks the score) • Open mathProblem.php in the sessions folder: Chapter 12

34. Managing a Web Session:It Takes a Lot of Planning! • It takes a lot of planning to design a Web session. • You will probably need a lot of selection structures. • Your code must allow for: • Any events that are included in the session. • Unexpected user actions. • For example, what if the user returns to the session's first page, and this page resets their score to 0, or goes directly to a page that assumes the user has previously entered their name on another page? • Your code should handle all possible user actions.. Chapter 12

35. Managing a Web Session: The isset() Function • Recall that the isset()function tests whether or not a variable has already been created. • This is useful to decide what action should be taken on a Web page. • To set the score to 0 only once in a session: if (!isset($_SESSION['playerScore'])) $_SESSION['playerScore'] = 0; • To ensure the user has already provided a name: if (!isset($_SESSION['playerName'])) print("<a href=\"start.php\">Go to start page</a>"); Chapter 12

36. A Note About Session Security • When a user opens a Web page that initiates a session, the Web server creates a unique identification (UID) number for the session. • Although many users might access the Web application at the same time, the server uses the UIDs to distinguish between each user’s session. • The data for each user is automatically maintained in a separate $_SESSION array associated with the user's UID. Chapter 12

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